The present invention relates to a novel vinyl chloride copolymer and a vinyl chloride copolymer composition, and more particularly to a copolymer of vinyl chloride or a monomer mixture containing vinyl chloride with 1,2-polybutadiene oligomer and/or epoxidized 1,2-polybutadiene oligomer, and a composition containing the vinyl chloride copolymer.
Polyvinyl chloride is employed widely, since it is inexpensive as compared with other synthetic resins and moldings made thereof have various excellent physical properties. Plasticization of polyvinyl chloride by the addition of a plasticizer is a well known technique for providing soft and rubber-like articles. However, usual plasticized polyvinyl chlorides cannot be employed in a field requiring a low compression set, e.g. packings, since it is impossible to lower the compression set of moldings. Accordingly, various improvements of polyvinyl chloride have been attempted for lowering the compression set. One of these attempts is the improvement based on cross-linking techniques by copolymerization of vinyl chloride with a cross-linking agent, e.g. (1) copolymerization of vinyl chloride with a divinyl compound such as butadiene, isoprene or divinylbenzene, (2) copolymerization of vinyl chloride with a diallyl compound such as diallyl phthalate or diallyl maleate, (3) copolymerization of vinyl chloride with a dimethacrylate such as diethylene glycol dimethacrylate, and (4) copolymerization of vinyl chloride with a 2,5-divinyltetrahydropyran derivative. However, the cross-linked polymers obtained by such a copolymerization have high melting points and do not melt with ease, and as a result, the unmolten fine polymer particles remain in the obtained moldings, resulting in lowering of tensile strength due to stress concentration to that portion. This tendency is particularly noticeable in plasticized resin systems with a plasticizer. The preparation of the above-mentioned cross-linked polymers has been scarcely practiced industrially, because the cross-linked polymers have the defect as mentioned above.
It is an object of the present invention to provide a vinyl chloride copolymer which can be molded into articles having excellent creep characteristics, particularly having a low compression set.
A further object of the present invention is to provide a vinyl chloride copolymer which has a good processability and gives flexible moldings having excellent creep characteristics, particularly a low compression set, without lowering a tensile strength.
Another object of the present invention is to provide a vinyl chloride copolymer composition capable of giving soft moldings having excellent creep characteristics, particularly a low compression set, without lowering a tensile strength.
A further object of the present invention is to provide a vinyl chloride copolymer composition capable of giving hard moldings having a delustered surface without conducting a delustering operation.
These and other objects of the present invention will become apparent from the description hereinafter.